It is well known that a pressurized flow of abrasives can be employed to clean metal surface prior to painting or coating. The typical system uses compressed air to transport the abrasive, such as sand grains, through pipe and hoses to a nozzle that accelerates the abrasive against the surface of the object to be cleaned. Such object may be a pipe line, bridge, ship, floor, roof, railroad car or the like. More recent cleaning systems have used water in combination with an abrasive to suppress dust production and to wash the object as it is otherwise cleaned of contaminants.
However all such systems are believed to have a number of shortcomings. For example, prior systems have not, to applicants' knowledge had interlocked controls so that such systems could be started and stopped by a deadman-type control at the blast nozzle, and thus were somewhat unsafe and unreliable in operation. Other systems have not had any provision for saving the pump by shutting down its operation in case input water levels are low, so that the pump was subject to wear and high maintenance requirements. Still other systems have not had an optimum inhibitor injection system that worked automatically in association with the pump so that a proper amount of inhibitor is mixed with the water stream to prevent accidental flash rusting of the metal being cleaned. No system that applicants are aware of has had the capability to operate two blast nozzles independently of one another, and in multiple modes of operation depending upon the requirement of the particular cleaning operation. In summary, applicants believe that prior cleaning systems of the type to which this invention relates have not been constructed in a manner to provide safe, clean, fast and effective cleaning of contaminated metal surfaces, and it is to these general requirements that the present invention is directed.
It therefore is the general object of the present invention to provide a new and improved control system for a liquid-propelled abrasive cleaning apparatus that obviates the above-mentioned disadvantages of prior systems.